The bulbourethral glands are a pair of small, pea-sized structures tucked behind the urethra in the male pelvis, and their main job is producing the clear, slippery fluid that sometimes appears at the tip of the penis during sexual arousal. Often called Cowper’s glands after the English anatomist who described them in detail in 1699, they play a quiet but real role in reproductive biology, urinary comfort, and occasionally clinical medicine. Despite being among the smallest organs in the male reproductive tract, they sit at the center of surprisingly persistent questions about contraception, infection, and even cancer.
Location, Structure, and What the Gland Looks Like Under a Microscope
Each bulbourethral gland is roughly the size of a pea and sits within the muscle of the pelvic floor, just behind the section of urethra that runs through the base of the penis (the bulbar urethra). A short duct from each gland empties into the urethra itself. The glands are classified as compound tubuloalveolar glands, meaning they have branching clusters of secretory units that drain into a shared duct system, similar in architecture to salivary glands.
Histological studies in several mammalian species show a consistent basic design. Each gland is wrapped in a capsule of dense connective tissue that sends partitions inward, dividing it into lobules. Within each lobule, the secretory units are lined by a single layer of mucus-producing cells whose nuclei sit at the base of the cell, with the rest of the cell packed with secretory granules. Those granules contain neutral and acidic mucosubstances, the raw material for the viscous, lubricating fluid the gland produces.1PubMed. Structural and ultrastructural features of boar bulbourethral glands The excretory ducts that carry the secretion out of the gland are also lined by a single layer of epithelium, though their cells look slightly different from the secretory cells deeper inside.2PubMed. Gross, histological and ultrastructural features of the bulbourethral gland in the greater cane rat (Thryonomys swinderianus)
What the Gland Secretes and Why It Matters
During sexual arousal, the bulbourethral glands release a thick, clear mucus into the urethra. This fluid is commonly called pre-ejaculate or “pre-cum.” Its best-established function is to neutralize any residual acidity left behind by urine, making the urethra a friendlier environment for sperm that will pass through during ejaculation.3PubMed. A neglected gland: a review of Cowper’s gland Urine is naturally acidic, and sperm are sensitive to pH, so this preparatory rinse likely contributes to sperm survival during their brief transit.
The fluid also acts as a lubricant for the urethra and, to some extent, the glans of the penis. The volume produced varies quite a bit from person to person, from barely noticeable to several milliliters. The mucus itself is rich in glycoproteins, giving it its characteristic slippery texture. Beyond the bulbourethral glands, seminal plasma as a whole is a mix of secretions from the testes, epididymis, prostate, and seminal vesicles, containing ions, enzymes, proteins, hormones, and even extracellular vesicles carrying DNA and RNA.4PubMed Central. Seminal Plasma: Relevant for Fertility? The bulbourethral glands contribute a relatively small share of total ejaculate volume, but their secretion arrives first, priming the pathway before the rest follows.
How the Gland Is Controlled
Like most glands involved in sexual function, the bulbourethral glands receive nerve signals from both the autonomic nervous system (the involuntary division that handles things like heart rate and digestion) and the somatic nervous system (which governs voluntary muscle control). Research in rats has shown that somatic nerve pathways contribute to the release of the gland’s secretion, working alongside autonomic signals delivered by the cavernous nerve. The autonomic component appears involved in both producing the secretion and contracting the smooth muscle around the gland to push it out, while the somatic component adds a second layer of control over the release itself.5PubMed. Somatic innervation contributes to the release of bulbourethral gland secretion in male rats
This dual nerve supply helps explain why the timing of pre-ejaculatory fluid varies so much from one person to another and even from one occasion to the next. Arousal intensity, the degree of physical stimulation, and individual nervous system wiring all influence how much fluid appears and when.
Can Pre-Ejaculate Cause Pregnancy?
This is probably the most commonly asked question about the bulbourethral glands, even if people do not realize they are asking about a gland at all. The short answer: it depends on the person and the circumstances, and researchers have gone back and forth on this for over two decades.
An early study of pre-ejaculatory samples from men undergoing fertility evaluation found no sperm in any of them, leading the authors to conclude that pre-ejaculate from Cowper’s gland “cannot be responsible for pregnancies during coitus interruptus.”6PubMed Central. Does preejaculatory penile secretion originating from Cowper’s gland contain sperm? That seemed to settle the question for a while. But a later study found that about 41% of participants produced pre-ejaculatory samples containing sperm, and in most of those cases the sperm were motile (capable of swimming). Interestingly, each man was consistent: those who had sperm in one sample had sperm in all their samples, and those who did not have sperm in one sample never did.7PubMed Central. Sperm content of pre-ejaculatory fluid
A 2024 pilot study tried to refine the picture by focusing specifically on men experienced with the withdrawal method. Among 70 paired samples from 24 men, sperm showed up in about 13% of pre-ejaculate specimens, from a quarter of participants. However, the researchers set a threshold for “clinically significant pregnancy risk” at a sperm concentration above one million per milliliter, and only seven samples cleared that bar. Their conclusion was that in “perfect-use” withdrawal, motile sperm in pre-ejaculate were usually absent or present in quantities too low to pose a meaningful pregnancy risk.8PubMed. Low to non-existent sperm content of pre-ejaculate in perfect-use contraceptive withdrawal, a pilot study
The apparent contradiction between studies probably comes down to two things. First, the sperm found in pre-ejaculate are not produced by the bulbourethral glands themselves. These glands make mucus, not sperm. Any sperm present in pre-ejaculate are leftovers from a prior ejaculation that were still sitting in the urethra, or sperm that leaked ahead of the main ejaculation. Second, the “consistent producer” pattern found in one study suggests that anatomical differences between individuals, perhaps in how efficiently the urethra clears after ejaculation, may determine who carries sperm in their pre-ejaculate. For anyone relying on the withdrawal method, the practical takeaway is that pre-ejaculate can contain sperm and the risk is not zero, but it appears to be substantially lower than the risk from ejaculation itself.
Pre-Ejaculate and HIV Transmission
A related concern involves whether pre-ejaculatory fluid can carry HIV. A study of 60 HIV-positive men examined blood, semen, and pre-ejaculate for detectable virus. Among men not on suppressive antiretroviral therapy, one out of eight had detectable HIV in his pre-ejaculate. More reassuringly, among 52 men whose blood viral load was undetectable on treatment, none had HIV detected in their pre-ejaculate, even though about one in five still had detectable virus in their semen.9PubMed Central. HIV-1 is undetectable in pre-ejaculatory secretions from HIV-1-infected men on suppressive HAART
The finding that pre-ejaculate appears virus-free when treatment keeps blood viral load undetectable aligns with the broader “undetectable equals untransmittable” public health message. But it also highlights that without effective treatment, pre-ejaculate is not necessarily safe, and that semen itself may harbor virus even when blood tests look clean. From a public health perspective, pre-ejaculate is one more reason to treat HIV early and consistently.
Syringoceles and Other Structural Problems
The most common clinical condition involving the bulbourethral glands is a syringocele, a cystic dilation of the gland’s duct. The name comes from Greek: “syringo” (tube) plus “cele” (swelling). These were first described and classified based on observations in boys and were originally thought to be mainly a pediatric issue, but more recent work has shown that they occur in adults as well and may be more common than previously recognized.10PubMed Central. Syringoceles of Cowper’s ducts and glands in adult men
Syringoceles come in several forms. The classic classification identifies four types:
- Simple: a minimally dilated duct.
- Perforate: a ballooned-out duct that still drains into the urethra, looking like a pouch or diverticulum.
- Imperforate: a duct that has swollen into a closed cyst sitting just beneath the urethral lining.
- Ruptured: the thin membrane left behind after a dilated duct has burst open into the urethra.
This classification was developed from a series of eight boys and has remained the working framework for decades.11PubMed. Cowper’s syringocele: a classification of dilatations of Cowper’s gland duct based upon clinical characteristics of 8 boys In clinical shorthand, syringoceles are also grouped as “open” (communicating with the urethra, allowing urine to flow back into the cyst) or “closed” (sealed off, forming a cyst-like swelling in the urethral wall).12PubMed. Cowper’s syringocele: symptoms, classification and treatment of an unappreciated problem
Symptoms can include a weak urinary stream, dribbling after urination, recurrent urinary infections, and occasionally blood in the urine. Many syringoceles, especially the simple type, cause no symptoms at all and are found incidentally. When imaging is needed, retrograde urethrography (a contrast study of the urethra) is the standard test for open syringoceles, while MRI offers better detail for assessing the full extent of the abnormality.13PubMed. Imaging of the Bulbourethral (Cowper) Gland: Abnormalities and Differential Diagnosis
When a syringocele does need treatment, endoscopic surgery is preferred over open surgery. The standard approach is unroofing the cyst through a scope passed into the urethra, using either a cold knife or a holmium laser to open the wall. Studies report good outcomes, with patients free of symptoms a year out.14PubMed Central. A Case of Symptomatic Cowper’s Syringocele in an Adult Male: Diagnosis and Management15PubMed Central. Cowper’s Syringocele in Adolescent Male: Case Report
Infections of the Bulbourethral Gland
Inflammation of a bulbourethral gland, called cowperitis, is uncommon but can be serious when it does occur. The symptoms overlap with other pelvic infections: intense perineal pain, difficulty urinating, fever, and general malaise. On physical examination, a doctor may feel thickening in the tissue between the rectum and the urethra during a rectal exam. In severe cases, the gland can develop an abscess.16PubMed Central. Acute uropathogen-related cowperitis with sepsis: case report and literature review
Historically, the bacteria most associated with cowperitis were sexually transmitted organisms like gonorrhea and chlamydia. In recent decades, the microbial picture has shifted. Common urinary tract pathogens such as E. coli and Pseudomonas are now more frequently implicated, though sexually transmitted infections remain part of the picture.17PubMed Central. Acute uropathogen-related cowperitis with sepsis: case report and literature review A chronic infection can sometimes lodge in the gland, especially when an underlying structural problem like a syringocele creates a pocket where bacteria can persist despite antibiotics.18Urology Case Reports. Sepsis secondary to Cowper’s gland abscess When an abscess forms, antibiotics alone may not be enough; direct drainage of the abscess is often required to clear the infection and prevent it from progressing to sepsis or creating a fistula (an abnormal channel to the skin).
Cancer of the Bulbourethral Gland
Cancer arising from the bulbourethral gland is extraordinarily rare. As of 2014, only nine cases had been described in the medical literature.19PubMed Central. Metastatic Cancer of Cowper’s Gland: A Rare Cancer Managed Successfully by Molecular Profiling The rarity means there are no clinical trials to guide treatment, and each reported case has been managed individually. One published case involved a 25-year-old man with no other health conditions who was treated with surgical removal of the proximal urethra, sphincter, and prostate, followed by reconstruction of the urinary tract, without needing chemotherapy or radiation because the surgery was considered complete.20PubMed. Bulbourethral gland adenocarcinoma in a 25-year-old man without comorbidities: radical resection of proximal urethrae with Mitrofanoff-type appendicovesicostomy In another case involving metastatic disease, molecular profiling of the tumor was used to select targeted treatments, and the patient was managed successfully over seven years using that approach.21PubMed Central. Metastatic Cancer of Cowper’s Gland: A Rare Cancer Managed Successfully by Molecular Profiling
Because so few cases exist, there is no screening protocol and no established risk factors for bulbourethral gland cancer. It is diagnosed when symptoms (typically obstruction or a mass in the perineum) prompt investigation and biopsy. The extreme rarity means that almost no urologist will encounter it in a career, and treatment decisions are necessarily improvised based on the tumor’s behavior and molecular characteristics.
How the Glands Change with Age
Like many glandular tissues, the bulbourethral glands undergo gradual involution (shrinkage and reduced activity) as men age. A study tracking gland tissue from adolescence through old age found that the secretory cells get shorter, the secretory units shrink in cross-section, and the overall proportion of functional gland tissue (parenchyma) decreases steadily. The activity of the secretory cells, measured by the density of their cytoplasm, peaks in young men and declines by the first period of adulthood, with a further drop into old age. Even in elderly men, though, the cells still contain PAS-positive material, a staining marker indicating that they retain at least some ability to produce secretion.22Journal of Anatomy and Histopathology. Age-Related Involution of the Human Bulbourethral Glands and Benign Prostatic Hyperplasia
This gradual decline may partly explain why older men sometimes notice less pre-ejaculatory fluid than they did when younger. The glands do not suddenly stop working, but their output diminishes in parallel with other age-related changes in the reproductive tract.
The Glands Across Species
Bulbourethral glands are not unique to humans. They are found across a wide range of mammals, though their size, number, and relative importance vary considerably. In some species the glands are proportionally much larger than in humans and contribute a substantial fraction of the ejaculate. Comparative work on bat species from the family Phyllostomidae found that all five Brazilian subfamilies studied possessed a pair of extra-abdominal bulbourethral glands as part of their reproductive accessory gland complex. Interestingly, these bats lack seminal vesicles entirely, and their prostates show different regional structures depending on the subfamily, suggesting that the relative contributions of each accessory gland have been reshuffled repeatedly during evolution.23PubMed Central. Comparative analysis of the male reproductive accessory glands of bat species from the five Brazilian subfamilies of the family Phyllostomidae (Chiroptera)
In boars, the bulbourethral glands are enormously developed and produce a gel-like fraction of semen that forms a plug in the female reproductive tract after mating, a function that has no equivalent in human reproduction. The basic cellular architecture remains strikingly similar across species, however, with the same mucus-producing cell type, basally positioned nuclei, and lobular organization seen in humans, rodents, and livestock alike.24PubMed. Structural and ultrastructural features of boar bulbourethral glands
Who First Described Them
The naming history of the bulbourethral glands is a minor case study in how medical credit gets assigned. According to a historical review, the glands were first mentioned in the scientific literature in 1684, in an edition of the French journal “Journal des sçavans,” credited to the French surgeon Jean Méry. Fifteen years later, in 1699, the English anatomist William Cowper published the first detailed description of the glands’ structure, location, and function.25PubMed. The history of discovery of bulbourethral glands It was Cowper’s name that stuck, and “Cowper’s glands” remains the most common informal term in clinical use, even though Méry’s observation came first. The formal anatomical name, bulbourethral glands, describes their location relative to the bulb of the urethra and avoids the priority debate altogether.